Do prostacyclin and thromboxane contribute to the “protective effect” of pregnancies with chronic hypertension? A preliminary prospective longitudinal study

OBJECTIVE: The aim of this study was to assess prospectively the urinary excretion of renal and systemic metabolites of thromboxane and prostacyclin in normotensive and chronic hypertensive pregnancies. STUDY DESIGN: Pregnant hospital employees were invited to collect 24-hour urine samples weekly from the seventh week until delivery. Concentrations of renal metabolites (thromboxane B₂, 6-keto-prostaglandin F_1α) were measured by radioimmunoassay after extraction. Systemic metabolites (2,3-dinor-thromboxane B₂, 2,3-dinor-6-keto-prostaglandin F_1α) were assessed by enzyme immunoassay after extraction and high-pressure liquid chromatographic separation. RESULTS: Thromboxane B₂ excretion was similar in normotensive and hypertensive pregnancies, whereas a twofold increase of 6-keto-prostaglandin F_1α was observed in hypertensive compared with normotensive pregnancies (7537 ± 349 vs 3857  ± 202 pg/mg creatinine, p < 0.001). During pregnancy in both conditions measurements displayed uniform excretion of thromboxane B₂ with progressively increased levels of 6-keto-prostaglandin F_1α in chronic hypertension (R² = 0.60, p < 0.005). Mean excretion of 2,3-dinor-thromboxane B₂ averaged 1208 ± 65 and 898 ± 48 pg/mg creatinine in normotensive and hypertensive pregnancies (p < 0.001), mainly due to significant decreased concentrations in hypertension in the first half of pregnancy. Conversely, 2,3-dinor-6-keto-prostaglandin F_1α levels were 845 ± 39 and 1226 ± 67 pg/mg creatinine in normotensive and hypertensive pregnancies (p < 0.001), mostly because of significantly increased production in hypertension from 22 weeks onward. Ratios of both renal and systemic metabolites favored increased prostacyclin production in chronic hypertension. CONCLUSION: In contrast to preeclampsia, uncomplicated mild to moderate chronic hypertensive pregnancies are characterized by an excess production of prostacyclin with unaltered or even lower thromboxane concentrations, which may contribute to the general favorable outcome of this hypertensive condition.(Am J Obstet Gynecol 1997;177:1483-90.)